Altimeter



April 16, 1946.

P. F. SHIVERS ALTIMETER Filed Dec. 18 1942 2 Sheets-Sheet l A ril 16,1946. P. F. SHIVERS ALTIMETER Filed Dec. 18, 1942 2 Sheets-Sheet 23nneutor IWUL f .5h'lVE/T5 (Ittorneg Patented Apr. 16, 1946 ALTIMETERPaul F. Shivers, Edina, Minn., assignor to Minneapolis-HoneywellRegulator Company, Minneapolis, Minn., a corporation of DelawareApplication December 18, 1942, Serial No. 469,398

17 Claims.

The present invention relates to pressure measuring devices of the typefor indicating the magnitude of quantities by measuring the density of agas mass whose variable density is parametric of the quantity whosemagnitude is to be indicated. and more particularly to a measuringinstrument of a type such as discussed in my copending applicationSerial No. 466,283 filed November 20, 1942.

My invention is particularly adapted for use in the measurement ofaltitudes and is of a type wherein the altitude indication dependsdirectly on the static, that is, barometric, atmospheric pressure. Asdiscussed in detail in my above noted application, the altitudeindication of such an instrument is influenced directly by the densityof the gas mass and indirectly by the efiect of the temperature of thegas mass on its density.

For the sake of uniformity in instrument dial calibration, certainarbitrary values of density and temperature have been selected to definea standard atmosphere. This standard atmoshere is of such density as togive a barometric pressure at a point one foot above sea level equal tothat of a column of mercury 29.92 inches high. The temperature gradientin the standard atmosphere is such that at sea level the temperature is59 F., while the temperature is 67 F. at the bottom of an isothermallayerlwhich has been found to exist at a variable height which isapproximately 35,000 ieet in middle latitudes. In this standardatmosphere the barometric pressure has been found to have an inverselogarithmic relation to the altitude above sea level.

The atmosphere surrounding a craft in flight is not normally thestandard atmosphere, however, but differs therefrom in sea level staticpressure and in temperature gradient. Thus, when the temperature dropfor a given increase in altitude is greater than the assumed standardfor which the measuring instrument may be calibrated, in order toapproximate the true altitude an increase in the altitude indicationbased upon such assumed standard must be made, as shown graphically inthe aforenoted co-pending application, the amount of such increase isdependent upon the altitude at which such correction is made.

Further, where the temperature drop is less than that for the assumedstandard for which the device is calibrated a decrease in the altitudeindication must be made in an amount likewise dependent upon thealtitude level at which such correction is made.

It is an'object of my invention therefore to provide normal controlmeans whereby an altitude indication resulting solely from staticpressure may be corrected for atmospheric temperature conditions so thatsuch corrected altitude indication may more nearly approximate th'etruealtitude.

Another object of my invention is to provide mechanical means responsiveto atmospheric temperature conditions for applying a, biasing force toan atmospheric pressure responsive measuring member so as to compensatesaid member for changes in atmospheric pressure due to a, change intemperature.

Another object of my invention is to provide variable cam means forcontrolling the application of such a biasing force to the responsivemember in response to atmospheric pressure and temperature conditions orin response to either of said conditions separately.

Another object of my invention is to provide means responsive toatmospheric pressure conditions for applying a biasing force to atemperature responsive measuring member so as to vary the'temperaturecompensation afforded thereby in accordance with the atmosphericpressure level at which said compensation is applied.

Another object of my invention is to provide an improved impedancetransmitter device for electrical control systems including a movablearmature member and a movable core member, each of which is separatelyadjustable in position with relation to the other under the influence ofindependent condition responsive devices; said control memberscooperating so as to differentially accomplish a single function.

A further object of my invention is to provide in such an impedancetransmitter device connection means whereby one of said members may becontrolled by atmospheric pressure responsive means and the other membermay be con troller by atmospheric temperature responsive means forcorrecting the indicated altitude of an altimeter for changes intemperature.

Further objects and advantages of this invention are set forth inthefollowing description,

taken with the accompanying drawings, and the novel features thereof arepointed out in the appended claims. The disclosure, however, isillustrative only and I may make changes in detail, especially inmatters of shape, size, and arrangement of parts within the principle ofthe invention, to the full extent indicated by the broad generalmeanings of the terms in which the appended claims are expressed.

In the accompanying drawings wherein like of the various figures.

Figure 1 represents diagrammatically one form of my invention,

Figure 2 represents a modified form of my in vention,

Figure 3 represents an enlarged detailed view of my improved impedancetransmitter.

In the form of my invention illustrated in Figure 1 there is provided animpedance bridge circuit indicated generally by the numeral l8 andincluding variable resistances l and 2 and impedance coils 3 and 4. Theresistance I is connected to the impedance .coil 3 by a conductor 8while the resistance 2 is connected t the impedance coil 4 by aconductor 9.

The conductors 8 and 9 are further connected by conductors l4 and I5 toa secondary winding l8 of a transformer IT, as at input terminals I2 andI3 respectively. Primary winding |8 of the transformer is connected byconductors |9 and 2|! to a suitable source of alternating currentwhereby an alternating current is induced through transformer action inthe secondary winding l6 and passes through theconductors l4 and |5 toinput terminals l2 and I3 of the bridge circuit I0.

Coils 3 and 4 as shown in Figure l are connected to an output terminal2| to which there is in turn connected an output conductor 22, while thevariable resistances and 2 are connected to an output terminal 23 towhich there is in turn connected an output conductor 24. The outputconductors 22 and 24 are connected to input terminals 25 and 26 of asuitable amplifier indicated by the numeral 21.

It will be readily seen that the coils 3 and 4 form two arms of thebridge circuit Ill. The variable resistance windings I and 2 form theopposite arms of the bridge circuit Ill.

Coacting with the coils 3 and 4 is a movable core or armature 28 ofmagnetic material. Core 28 is operably connected by a rod 29 toatmospheric pressure responsive member or aneroid 30.

The bridge circuit I0 is so arranged that normally with core 28positioned substantially equally within the two coils 3 and 4 the bridgecircuit I0 is balanced and no signal potential appears across outputterminals 2| and 23.

However, upon a decrease in atmospheric pressure causing the expansionof the aneroid 30, core 28 moves upward. The core 28 then ap proachesfurther toward or extends further into the coil 3 and correspondinglymoves further from or projects less into the other coil 4. The magneticflux through the coil 3 increases, increasing the impedance of the coil3. 0n the other hand, the flux through the coil 4 decreases,

decreasing the impedance of the coil 4 and causing the potential of theoutput terminal 2| to shift from a value half way between that of inputterminals l2 and I3 to a value somewhat closer to that of input terminalI3. The potential of output terminal 23, however, is not changed:therefore a potential difference exists between output terminals 2| and23, and the time phase of this potential difference is the terminal 2|were connected directly to input terminal I3 and output terminal 23 wereconnected directly to input terminal l2. This potential difference isfed through output conductors 22 and 24 to input terminals 25 and 28 ofamplifier 2 Further, upon an increase in atmospheric pressure causingcontraction of aneroid 30 and theresame as if output referencecharacters indicate corresponding parts from a value exactly half waybetween that of input terminals l2 and 3 to a value some at closer tothat of input terminal |2. The pot tial of output terminal 23, however,is not changed; therefore a potential difference existsbetween terminalsl2 and I3, and the time-phase of this potential difference is the sameas if terminal 2| were connected directly to terminal I2 and terminal 23were connected directly to terminal l3. This potential difference isthen fed directly to terminals 25 and 28 of amplifier 21 throughconductors 22 and 24. i

The amplifier 21 may be of any suitable type of electronic amplifierwell known in the art such as shown for example in Patent No. 1,586,233grantedMay 25, 1926, to AnschutZ-Kaempfe or may be preferably anelectronic amplifier of the type shown and described in the co-pendingapplication of Albert P. Upton, Serial No. 437,561, dated April 3, 1942.The amplifier 21 is provided, as previously described, with the inputterminals 25 and 28 and is further provided with output terminals 3| and32.

A motor 33 is shown as being of the split phase type having a pair offield windings 34 and 35. Winding 35 is connected by the conductors 36and 31 to the output terminals 3| and 32 of the amplifier 27.

A transformer 38 is provided for energizing the motor winding 34, saidtransformer having a primary winding 39 and a secondary winding 40.Primary winding 39 is connected by conductors 4| and 42 to conductors l8and 28 which are in turn connected to a suitable source of alternatingcurrent. Current is supplied to secondary winding 40 through transformeraction from the primary winding 38. Motor winding 34 is continuouslyenergized from the secondary winding 40 of the transformer 38. Acondenser 43 is connected'in series between the secondary winding 40 andthe motor winding 34 and causes a phase displacement of substantially 90between the current flowing in the winding 34 and the terminal voltageof the secondary winding 40.

As described in detail in the 'co-pending Upton application previouslyreferred to, amplifier 21 is of the type which produces in the branch ofthe output circuit including conductors 36 and 31 and motor winding 35an alternating current of the same phase as the potential applied toinput terminals 25 and 26. Since transformer primary windings l8 and 39are both connected to the same alternating current supply lines l9 and20, it will be understood that the potential appearing at the terminalsof the secondary windings l6 and 40 are of the same phase. The currentflowing through winding 34 is, however, shifted substantially electricaldegrees with respect to this potential by the condenser 43 as previouslyexplained. The winding 35 on the other hand, is supplied with currenteither in phase or -out of phase with the terminal potential of windingsl6 and 48 depending upon the direction of unbalance of the bridgecircuit Hi.

In accordance with the well known characteristics of a split phasemotor, when the windings 34 and 35 are supplied with current 90 out ofphase, the motor 33 i caused torotate in a predetermined direction. Theoperation of a split phase motor of the type described herein isdescribed in the oo-pending Upton application previously referred to.

The motor 33 is adapted to drive a shaft in a direction depending uponthe unbalancing oi the bridge circuit l9 and the resultantcurrentsupplied from the amplifier 21 to the motor 33.-

The shaft 44, in turn, is adapted by suitable means such as a gear train45 to drive an indicator means 46, which is of a suitable type wellknown in the art. Moreover, the motor 33 is further adapted by suitablemeans such as a shaft 44, train of gears 45 and shaft 41, to turn a cam49 so as to adjust the tension of a loading spring 49 for purposes whichwill hereinafter be explained. The cam 49 cooperates with a roller 59mounted on the loading spring 49 for the adjustment of the tension ofthe spring 49. The loading spring 49 is pivoted at one end on a fixedknife edge and engages aneroid 39 at a portion 19 intermediate theopposite ends, exerting a.

tension thereon dependent upon the adjustment of the spring 49.

It will thus be seen that upon a decrease in pressure the aneroid 39expands forcing the rod 29 upward against the tension of the spring 49.Moreover, such upward movement of the rod 29 likewise moves the core 28upward which, as previously explained, increases the impedance of thecoil 3 and decreases the impedance of the coil 4 and thereby causes anunbalancing of the variable reluctance bridge circuit l9. The unbalancepotential is amplified by the amplifier 21 in a manner previouslydescribed and the resultant amplified electro-motive force drives themotor 33' so as to rotate the shaft 44 in a direction to cause actuationof the indicator means 46 in a manner well known in the art so as toindicate an increase in altitude. Moreover, the motor 33, upon suchunbalancing of the bridge circuit l9, turns the shaft 44, shaft 41, andintermeshing gear means so as to turn the cam 48 in a counterclockwisedirection so as to cause a downward movement of the roller 59, therebyincreasing the tension exerted by the spring .49 on the aneroid 39. Thisin turn causes a contraction of the aneroid 39, under atmosphericpressure and the additional tension of the loading spring 49. to causedownward movement of the rod 29 until the core 29 is once againpositioned in such a manner that bridge circuit I9 is balanced,whereupon the signal potential across output terminals 2| and 23disappears, and motor 33 ceases the actuation of the cam 49 and theindicator means 46.

Further, upon an increase in atmospheric pressure above the balancingpoint of the bridge circuit l9 as in the case of a decrease in altitude,the aneroid 39 contracts, causing a downward movement of the rod 29 andhence causing the core 28 to increase the impedance of coil 4 and todecrease the impedance of coi1 3. The amplified potential resulting inthe unbalance of circuit l9 now causes rotation of the motor 33 in adirection opposite to that in the precedin paragraph, moves theindicator means to indicate a decrease in altitude and moves cam 48 in aclockwise direction so as to decrease the tension of the loading spring49. The decreasing tension of the spring 49 permitsexpansion of theaneroid 39 and upward movement of core 28 to a position such that thebridge circuit is again balanced.

whereupon the signal potential disappears and action of the motor 33terminates. The movement of motor 33 will thus stop until such time asthe bridge circuit I9 is once again unbalanced.

The cam 49, which turns in a counter-clockwise direction as the altitudeincreases, is so shaped that the pitch or the actuating cam surfacedecreases as the cam is rotated. so as to progressively decrease theincrement of vertical displacement applied to the roller 39 per unit ofatmospheric pressure change as the altitude readings of the indicatorincrease. Thus, at round level, the cam 49 ispositioned as shown inFigure 1 with the roller contacting the cam surface near its on 01'minimum radius 53, and upon a decrease in pressure the aneroid 39expands upward. Since the cam 49 is constructed so that at this pointthe relative movement of the cam 49 necessary to lower the roller 59 toincrease the spring tension 49 to balance the circuit per unit oipressure change is relatively slight, the indicator recordings for suchmovement are correspondingly slight per unit or pressure change.However, at relatively high altitudes with the cam 49 correspondinglyadjusted so that the roller 59 approaches the cam end 54. considerablygreater rotary movement of the cam 49 is necessary to cause suiilcientincrease in spring tension to turn the core 29 so as to balance thecircuit. This increases the necessary rotary movement of the shaft 41 tocause a correspondingly greater indicator movement per unit of pressurechange. This variation in the multiplication ratio of the indicatormeans as the altitude increases is necessary in order to approximate thetrue altitude, since as is well known in the art, the vertical distancetraveled for each unit of pressure change increases with the altitude.

In order to more accurately adjust the altimeter for the barometricpressure at the lower end of the air column from which the measurementis to be predicated, I have made the resistances l and 2 adjustable.Under assumed standard starting or ground level conditions they are ofequal resistance. The variable resistances i and 2 may be adjustedsimultaneously or separately, so that upon a decrease in barometricpressure at the starting level below the assumed standards theresistance I may be increased and the resistance 2 decreased inaccordance with a predetermined adjustment scale, thereby unbalancingthe bridge circuit i9 and causing a potential difference to appearacross output terminals 2| and 23. This potential is amplified, aspreviously explained, causing rotation of motor 33 so as to decrease thealtitude readings and to turn the cam 48 in a clockwise direction,rotation or the cam decreasing the ratio between indicator incrementsand units of pressure change, at the same time decreasing the tensionexerted by the loading spring 49 on the aneroid 39. The decrease intension of spring 49 in turn permits the core 29 to rise so that theimpedance of coil 3 is increased and the impedance of coil 4 de creasedto a point whereupon the bridge circuit [9 is once again balanced. Thus,correction may be effected for altitude readings which if uncorrectedwould be too high due to a decreasein the pressure of the air column atthe ground or starting level of the measurement Further, upon anincrease in the ground barometric pressure causing the altimeter at anassumed standard or operation to indicate an altitude below th truealtitude, the resistance I may be decreased and the resistance 2increased by suitable adjustment means in accordance with apredetermined adjustment scale unbalancing the previously balancedbridge circuit I so that a potential difference appears across outputterminals 2| and 23, which in turn causes motor 33 to rotate so as toturn the indicator 46 to increase the indicated altitude. The motor 33also turns the cam 48 in a counter-clockwise direction so as to increasethe ratio between indicator increments and units of pressure change atthe same time increasing the tension of spring 49 whereupon theatmospheric pressure acting upon the aneroid 30 together with theincreased tension of spring 49 forces the core 28 downward until theimpedance of coil 4 is increased and the impedance of coil 3 decreasedto a point whereupon the bridge circuit In is once again balanced. Theincrease of atmospheric pressure for the column of air above the assumedstandard is thus compensated and the indicator standard adjusted toincrease the altitude readings which would under the uncorrected assumedindicator standard be too low. Thus, the standard of operation of thealtimeter may be adjusted for the actual atmos pheric conditionsexisting at the ground or starting level of the measurement.

The structure which I have heretofore described in operation issubstantially the same as the structure previously described by me in myco-pending application Serial No. 466,283, filed November 20, 1942.However, there is disclosed in my present application a novel mechanicaltemperature compensating means not heretofore disclosed. Such means isprovided for varying the operative standard of the altimeter inaccordance with any deviation in the mean temperature from an assumedstandard.

As previously explained, an increase in mass atmospheric temperatureabove an assumed standard causes a higher indicated altitude at theassumed standard measure, attributable to the expansion of the mass orcolumn of atmospheric air caused by the increase in the temperature.Similarly, a decrease in mass atmospheric temperature below the assumedstandard causes a lower indicated altitude at the assumed standardmeasure, attributable to the contraction of the mass or column ofatmospheric air due to the decrease in temperature. Thus, it will beseen that under. a given set standard of operation varying altitudereadings may result at a given altitude level depending upon the stateof the air column, whether contracted or expanded.

In order to correct the operating standard or translation factor of thealtimeter for such errors. I have provided in the form of my inventionillustrated in Figure l a free air temperature responsive member 60which is shown as being of the fluid filled bellows type. The lower endof the member 60 has connected thereto a connection 6| formed of atubular material which connects with a free air thermometer bulb elementof the distance type indicated by numeral 62. The thermometer bulbelement 62 is structurally mounted so as to contact the free atmosphericair so that the fluid within the bulb element will respond to thetemperature of the free atmospheric air. It will thus be readily seen asis well known in the art that as the free air temperature decreases, thefluid within the thermometer bulb 62, tube BI, and bellows 60 will becaused to contract causing thereby the contraction of the bellows 60.Connected to the upper end of the bellows B is a rod 83 which hasconnected thereto one end 64 of a spring portion 65 of the leaf spring43. The opposite end of the leaf spring 49 is mounted on pivot 5| and.an intermediate portion 10 bears upon the aneroid 30. Mounted on theSprin portion 65 intermediate the portion 10 and end 84 is a roller 66adapted to engage a cam 81 which is in turn connected by a shaft 83 tothe cam 43. Thus, upon adjustment of cam 48 through the shaft 47, thecam 61 is likewise adjusted by the shaft 68. The cam 81 bears upon theroller 88 so as to vary the tension exerted by the spring portion 65upon the aneroid 30 in a manner similar to the action of the cam 43 androller 50 previously described.

In operation it will thus be seen that as the altitude increases asindicated by a decrease in atmospheric pressure the cam 48 rotates in acounter-clockwise direction together with the cam 81, increasing thetension applied on the aneroid 30 through the springs 49 and 65 forreturning the aneroid to zero or neutral position. Further, when thealtitude decreases as indicated by an increase in atmospheric pressurecams 4| and I1 rotate in a clockwise direction for decreasing thetension applied to the springs 85 and 48 so as to permit the return ofthe aneroid to its neutral or zero position. Indicator 46 driven by themotor 33 indicates the altitude corresponding to the increased ordecreased pressure at the aneroid 30.

However, in the event there is a deviation in the temperature of thefree atmospheric air from the assumed standard, aneroid 30 i subjectedto a force having the combined eifect of springs 65 and 49 and the forceof the atmospheric pressure. The atmospheric pressure in turn iscomprised of two components, the barometric pressure proportional to thealtitude according to the standard atmosphere, and a further pressure.which may be positive or negative, due to the difference between thedensity of air at the altitude and at the standard temperature and thatof air at the altitude and at the prevailing temperature. The positiontaken by the indicator in response to th resultant atmospheric pressure.as balanced by the tension in springs 49 and 65 must be furthercorrected by a factor proportional to the change in air pressure duesolely to its change in density with change in temperature. This factoris introduced by expansion or contraction of the bellows 60 in responseto changes in ambient temperature. On a drop in temperature, contractionof bellows 50 causes a decrease in the biasing force applied on the aneroid 30 through the spring portion 65, thus tending to allow core 28 tomove upward, unbalancing bridge circuit [0 and energizing the motor 33torotate the earn 48 and 51 in a counterclockwise direction and theindicator 46 so as to increase the indicated altitude. Such action,combined with the response of the device to changes in resultant airpressure, causes the aneroid 30 to return to its zero or normalposition.

Similarly, a decrease in the temperature of the free atmospheric air ata rat less than that for the assumed standard, or an increase intemperature, causes adjustment by the bellows 60 of the spring portion65 so as to increase the relative tension applied thereby upon theaneroid 30, causing thereby the relative downward movement of the core28 and accordingly a decrease in the reading of the indicator 46 and acorresponding movement of the earns 48 andv B1 in a clockwise directionso as to decrease the tension applied upon the springs 55 and 49,returning the aneroid 30 to a position where circuit I0 is balanced.

'The cam 61 is so shaped that the variation in temperature from anassumed standard will have a proper increased corrective effect as thealtitude increases. Thus such correction of altitude for temperatureapplied in accordance with the altitude level at hich such temperatureis measured. This is specifically accomplished by constructing the cam61 so that the pitch of the actuating cam surface varies in properproportion for the application of such temperature corrective factor asthe cam turn in response to change in atmospheric pressure or altitude.Thus as the altitude increases the rotarymovement of the cam 61necessary in combination with the cam -48 to cause the return of theaneroid 30 to the starting or bridge circuit I balanced positionincreases per unit of temperature change, thus increasing the correctionapplied to the indicator 46 per unit of temperature change as thealtitude increases.

I have shown that, under' standard tempera.. ture conditions, anincrease in altitude acts through aneroid 30 to unbalance bridge I0; theearns 48 and 61 then cause the leaf spring 49 and its spring portion 65to apply an increasing pressure on the aneroid 30 as the atmospherictemperature and pressure decrease in accordance with such standard andthus cause the operation of the indicator 46 under such assumed standardconditions.

However, if the temperature at a given altitude is greater than thestandard, expansion of bellows 60 increases the pressure of portion onaneroid 30. The magnitude of thi increase is of course dependent uponthe pressure level at which such measurement is made. Thi increase inspring tension compresses aneroid 30, resulting in the unbalancing ofthe bridge circuit I0. A decrease in the altitude reading of theindicator 46 thus results, earns 48 and 61 being simultaneously turnedin a clockwise direction by the motor 33 for return of the aneroid 30 soas to cause the rebalancing of the bridge circuit I0. Similarly anincrease in the altitude reading of the indicator 46 results upon theternperature at a given pressure level being less than that for thestandard. Thus I have provided novel means for compensating an altimeterfor temperature in accordance with the atmospheric pressure level atwhich such temperature is measured so that the indicated altitude ofsuch instrument may more accurately approximate the true altitude.

A second form of my invention is illustrated in Figure 2 wherein thereis provided an electronic control circuit similar to that previouslydescribed in Figure 1. There is provided, however, in Fi ure 2 a novelimproved impedance transmitter device indicated generally by numeralI50. My impedance device I50 includes a core member I00 mounted on thepivot member I0 I. Core member I00 is-of a generally E-shapedconfiguration. 0n the left and right E legs of the core member I00 aremounted impedance coils 3' and 4' corresponding to the impedance coils 3and 4 previously noted in regard to Figure 1.

Pivotally supported on the center leg of the core member I00 is anarmature member I02 mounted at one end of an adjustment arm I03. Theadjustment arm I03 is pivotally attached at I04 to one end of anactuating arm I05 which engages at the other end an aneroid I06 ofconventional form.

Mounted on the E-shaped core member F00 at one side of the pivot IN isan actuating arm I01 pivotally connected at I00 to one end of a linkmember I09. The link member I09 is connected at the opposite end to aspring I I0. Spring I I0 is fastened at III and arranged so as to tendto bias the E-shaped core member I00 in a counterclockwise directionabout the pivot IOI. An actuating arm H2 is pivotally connected at I I3to the link I09 and is pivotally connected at the opposite end at I I4to an arm II5 mounted at the movable end of a temperature responsivebellows I I6, The opposite end of the bellows I I0 is fixedly fastenedand has connected thereto at one end a conduit I I1 which connects atthe opposite end to a thermometer bulb IIB of the distance type which ispreferably mounted so as to contact the free atmospheric air. Providedin the bellows II6, conduit H1, and bulb H8 is an expansive fluid of atype well known in the art responsive to temperature whereby upon adecrease in temperature a relative contraction of the bellows IIGresults, while upon a temperature increase 9. corresponding expansion ofthe/bellows IIGoccurs. Such adjustment of the bellows II6 causes acorre-- sponding adjustment of the arm H5. The arm H2 is pivotallymounted intermediate the opposite ends thereof upon an adjustable pivotII! fixedly mounted on a sliding member I20 supported by a member I2Iand biased by a spring I22 towards the right as shown in Figure 21Provided at the right end of the slide I20 is a roller I23 rotatablymounted in a bifurcated arm I24. Under tension of the spring I22, theroller I23 engages the cam surface of a rotatable cam I25. The cam I25is attached by a shaft I26 to a second cam I21 driven by a shaft I28,mechanically connected by a" suitable gear train I29 to an indicator I30driven through a shaft I3I by a motor I32 as will be explained.

The cam I21 bears upon a roller I33 pivotally mounted on a leaf springI34 fastened at one end to a knife edge I35 and bearing at the oppositeend upon the aneroid I06. Upon an increase in altitude cams I21, I25 arerotated in a counterclockwise direction under the influence of motor I32and the cam I21 thereby increases the tension applied through the springI34 to the aneroid I06. The pitch of the actuating cam surface of thecam I21 decreases as the cam is turned in such a counter-clockwisedirection in a like manner to cam 48 previously explained in referenceto Figure 1.

Further, such counter-clockwise rotary movement of the cam I21 isaccompanied by a corresponding counter-clockwise movement of the cam I25which in turn causes a movement of the sliding member I20 towards theright as the altitude increases varying thereby the position of thepivot member H9 in relation to the arm II2. Of course suitableanti-frictional means may be provided between the pivot I I9 and the rodI I2 such as suitable bearings provided within a slotted portion of saidarm or other suitable means Well known in the art may be provided.However, for the purposes of illustration of my invention herein suchpivot II! is merely shown as of a knife edge structure.

Upon a decrease in altitude causing a clockwise movement of the cam I25the roller I23 follows the cam surface of the cam I25 under the tensionof the biasing spring I22 and thus the slide I20 is forced by the camI25 towards the left thereby shifting the pivot point I I9 in thisdirection. The pitch of the cam surface of cam I25 is arranged so as todecrease as the altitude increases so as to eifect the propertemperature compensation for each pressure level as previously e p inwith reference to cam 61 of Figure 1. It will thus be seen as thealtitude increases the pivot point of the lever H2 is shifted so as tovary the leverage exerted by the spring H and the bellows II 8 throughthe lever II2 on the link I00 so that at high altitudes a unit oftemperature change will cause a greater corrective efl'ect due to aleverage advantage than a corresponding unit 01' temperature change atlower altitudes and causing through the cooperation of cam I25 a moreaccu rate adjustment of the indicated altitude for each atmosphericpressure level.

Thus upon a temperature decrease the bellows IIB contracts, actuatingthe arm I I5, lever arm I I2, and link I09 against the biasing force ofthe spring IIO So as to in turn rotate the E-shaped armature in acounter-clockwise direction tending thereby to increase the air gapbetween the left arm or the core member I00 and the armature I02 and todecrease the air gap between the right arm of the core member I00 andthe armature I02. Obviously, upon an increase in temperature, thebellows IIB tends to expand causing movement or the arm II5, lever II:and link I09 under the biasing force of spring IIII so as to move theE-shaped core member in a clockwise direction thereby increasing the airgap between the right arm of the core member I00 and the armature I 02and decreasing the air gap between the left arm of the core member I00and the armature I02. The'purpose of such adjustment will be explainedhereinafter.

Similarly, upon an increase in altitude, causing thereby, a decrease inatmospheric pressure upon the aneroid I06, the aneroid I06 expandscausing the movement of arm I03 and armature I02 in a clockwisedirection about the center 'arm of the core member I00. Such movementcauses a lessening of the air gap between the armature I02 and the rightarm of the core member I00 and the widening of the air gap between thearmature I02 and the left arm member of the core member I00. .Anincrease in atmospheric pressure as upon a decrease in altitude causesan opposite adjustment of the armature I02 in a counterclockwisedirection about the center arm of the core member I00 causing thelessening of the air gap between the armature I02 and the left arm ofthe core member I00 while widening the air gap between the armature I02and the-right arm of the core member I00. The. purpose of such ad-J'ustment will be explained hereinafter.

Referring to the variable impedance device I50 the coil 3' is connectedat one end to the opposite end of the coil 4 by the electrical conductorI36. The other end of the coil 3' is connected by conductor 8' to an endof the variable resistance 2 while the other end of the coil 0' isconnected by a conductor 9' to an end of the variable resistance I'. Thevariable resistances I' and 2' are in turn connected together. Theconductors 8' and 9' are further connected at input terminals I2 and I0respectively by conductors I4 and I5 to a secondary winding I6 of atransformer IT. The primary II of the transformer is connected byconductors I9 and to a suitable source of alternating'current whereby analternating current is induced through transformer action into thesecondary winding I6 and through the conductors I4 and I5 to inputterminals I2 and I3.

It will be readily seen that the coils 3' form two arms of a bridgecircuit I0.

and 0' The'variable resistance windings I and 2' form the opposite armsof the bridge circuit I 0' and are adapted to be adjusted for groundatmospheric conditions. The coils 3' and 4 are wound in the samedirection and the electrical connections as will be readily seen aresuch that the magnetic flux produced by both coils 3' and 4' is of thesame polarity at any instant.

Coils 3' and 4 as shown in Figure 2 are connected to an output terminal2I' to which there is in turn connected an output conductor 22' whilethe variable resistances I' and 2 are connected to an output terminal23' to which there is in turn connected an output conductor 24. Theoutput conductors 22' and 24' are connected to input terminals 25 and26' of a suitable amplifier indicated by the numeral 21'. The amplifler21' is of a type previously described in relation to amplifier 27 shownin Figure 1.

A motor I32 is shown as being of the split phase type having a pair offield windings 05 and 30. Winding 35' is connected by conductors 36' and31 to the output terminals 3| and 32' of the amplifier 21'.

A transformer 38' is provided for energizing the motor winding 34', Thetransformer 38' having a primary winding 39' and a secondary winding40'. The primary winding 39 is connected through conductors II and 02'to conductors I9 and 20. A condenser 43' is connected in series betweenthe secondary winding 40' and the motor winding 34' and causes a phasedisplacement of substantially between the current flowing in the winding34' and the terminal voltage of the secondary winding 40. The motor I32upon an unbalancing of the bridge circuit I0 operates in a mannersimilar to motor 33 described in detail in reference'to Figure l andtherefore it is not deemed necessary to repeat such detaileddescription.

As previously noted the coils 3' and l are arranged so that the magneticflux produced by both coils 3' and 4' is of the same polarity at anyinstant. In other words, when the ilux produced by coil 3' is downwardin direction, the flux produced by coil 4' is also downward. Each coilmay therefore be said to produce a flux which tends to oppose the flowthrough that coil, of flux produced by the other coil.

The magnetic flux produced by coil 4' may be traced assuming the fluxdirection to be downward and moving in a counter-clockwise directionthrough the left leg 01' the core member I00, through the lower portionof the core member I 00 and up the center portion of the core member I00to the armature I02, left on the member I 02 and down across the air gapto the left leg of the core member I00.

, The magnetic flux produced by coil 3' may be similarly traced assumingthe direction downward and moving in a clockwise direction through theright leg of the core member I00 to the left along the member I 00 tothe center portion, up the center portion to the right along thearmature I02 and across the air gap to the right leg of the member I00.

With the parts in the position shown in the drawing of Figure 2 coremember I00 and the armature member I02 are in balanced position inrelation to each other and may be considered balanced.

However, upon movement of the armature I02 or the E-shaped core memberI00 as previously described so as to decrease the air gap between theright leg of the member I00 and the armature continuously thus thebridge circuit asoa-rro I02 and increases the air gap between the leftleg of the core member I and the armature I02, the flux through the coil3' is increased thereby increasing the impedance of the coil 3'. On theother hand, the flux through the coil 0' decreases, decreasing theimpedance of that coil. The bridge circuit Il' comprised of coils 3' and4' and resistances I and 2' thus becomes unbalanced due to the increasein the impedance of the coil 3' and the decrease in impedance of thecoil 4'. Therefore a potential difference exists between input terminals20' and 20' affecting the amplifier and motor I32 in a manner previouslydescribed in reference to Figure 1. Similarly, upon the armature I02 andthe core member I00 being shifted in relation to each other so as todecrease the air gap between the left leg of the core meme ber I00 andarmature I02 and increase the air gap between the right leg ofthe coremember I00 and armature I02, the impedance of coil 4' is increased andthe impedance of coil 3 is decreased, thereby causing an unbalancing ofthe circuit in the opposite direction.

Upon an increase in the impedance of coil 3' the motor means I32revolves in a direction so as to 4 turn the indicator I30 so as todesignate an increase in altitude while the cams I21 and I25 are rotatedin a counter-clockwise direction, thereby increasing the tension of thespring I3| for shifting the armature I02 back to a neutral position andshifting the pivot point I I0 towards the right thereby varying theefiect on the lever II2 of the spring H0 and bellows IIO so as tocounteract the biasing effect of the spring IIO. Thus the E-shaped coremember I00 is pivoted under force of the bellows IIG on pivot member MIin a clockwise direction and the armature I02 pivoted in acounter-clockwise direction so as to balance the impedance of the coils3' and 4'. As will be readily seen, such balancing effect may take placein response either to a relative increase in temperature of the freeatmospheric air or upon a decrease in atmospheric pressure applied atthe aneroid I00 or both.

Upon movement of the armature I02 and core member I00 so as to decreasethe air gap between the leit leg of core member I00 and armature I02,and increase the air gap between the right leg of core member I00 andarmature I02, the motor I32 will rotate in its opposite direction,thereby turning the indicator I30 so as to decrease the indicatedaltitude and turning the cams I21 and I25 in a clockwise direction. Suchaction decreases the tension applied by spring I34 upon the aneroid I00and shifts the pivot IIO toward the left thereby increasing the biasingeffect of spring I I0 upon the lever I I2 so that the lever I I2 may bemoved by spring I I0 so as to shift the core member I00 in acounter-clockwise direction while the armature I02 is moved in aclockwise direction by the expansion of the aneroid I06. This actionthen lessens the air gap between the right leg of the core member I00and armature I02 and increases the air gap between the left leg and saidarmature until the bridge circuit I0 is once again balanced. As will bereadily seen, such balancing effect may take place in response either toa relative decrease in the temperature of the free atmospheric air orupon an increase in the atmospheric pressure applied at the aneroid I00or both. I

It will thus be seen that I have rovided novel means for efiectingtemperature compensation in an altimeter. Although several embodimentsof position of said adjustable pivot so as to cause the invention havebeen illustrated and described in detail it is to be expresslyunderstood that the invention is not limited thereto, and that variouschanges may be made in the design and arrangements of the parts withoutdeparting from the spirit and scope of the invention as the same willnow be understood by those skilled in the art. For a definition of thelimits of the invention, reference will be had primarily to the appendedclaims.

I claim as my invention:

1. A device of the character described, comprising, in combination, avariable reluctance bridge circuit, an E-shaped core member, said coremember being pivotally mounted intermediate the opposite ends thereof,coils mounted on the end legs of said E-shaped core member, said coilsforming opposite legs of said bridge circuit, an armature pivotallymounted at the center leg portion of said E-shaped core member, anatmospheric pressure responsive device, an atmospherictemperaturerresponsive device, said armature being pivotally adjusted byone of said devices, and said core member being pivotally adjusted bythe other of said devices, said armature and said core member beingadiustably positioned for varying the impedance of said coils in such amanner as to unbalance said bridge circuit for performing a controlfunction.

2. A device of the character described, comprising, in combination, avariable reluctance bridg circuit, an E-shaped core member, said coremember being pivotally mounted intermediate the opposite ends thereof,coils mounted on the end legs of said E-shaped core member, said coilsforming opposite legs of said bridge circuit, an armature pivotallymounted at the center leg portion of said E-shaped coremember, anatmospheric pressure responsive device, ,an atmospheric temperatureresponsive device, said armature being pivotally adjusted by one of saiddevices, said core member being pivotally adjusted by the other of saiddevices, said armature and said core member being adjustably positionedfor varying the impedance of said coils in such a manner as to unbalancesaid bridge circuit, motor means energized upon the unbalancing of saidcircuit, indicator means operated by said motor means, control meansactuated by said motor means, and means connecting said control meanswith said E-shaped core member and said armature for rebalancing saidbridge circuit to terminate energization of said motor means.

3. A device of the character described, comprising, in combination, abridge circuit, a first member for controlling the electrical balance ofsaid circuit, said first member being controlled by an atmosphericpressur responsive device a second member for controlling the electricalbalance of said circuit, an arm for actuating said second member, anadjustable pivot for pivotally mounting said arm, an atmospherictemperature responsive device for actuating one end of said arm andtension means for actuating the opposite end thereof for causing theunbalancing of said circuit, motor means energized upon the unbalancingof said circuit, and control means actuated by said motor means forvarying the the movement of said arm in a direction for rebalancing saidcircuit so as, to terminate the action of said motor means.

4. A device of the character described, comprising,- in combination, abridge circuit, a first member, a second member positioned in spacedrelation to said first member, said members being adjustable withrespect to one another, atmospheric pressure responsive means foradjusting said first member in relation to said second member,atmospheric temperature responsive means for adjusting said secondmember in relation to said first member, saidmembers comprisinginductive impedancemeans included in said bridge circuit and meansreluctively altering the relative impedances of said impedance means,whereby upon responsive variations in the relationship of said memberssaid bridge circuit may be unbalanced, an indicator means, power meanscontrolled by said bridge circuit for actuating said indicator meansupon the unbalancing of said bridge circuit, control means actuated bysaid power means, and means connecting said control means with saidmembers whereby to alter their-relative adjustment for rebalancing saidbridg circuit to terminate the action of said power means on saidindicator means.

5. A device of the character described, comprising, in combination, aember movable in response to atmospheric pressure, a variable reluctancebridge circuit, a magnetic core mounted on said member and movabletherewith, said bridge circuit including members inductively associatedwith said core for cooperating therewith to control the electricalbalance of said bridge circuit, a first biasing means acting upon saidmember, an atmospheric temperature responsive device for varying theforc exerted by said first biasing means in response to atmospherictemperature conditions, a second biasing means acting upon said member,motor means controlled by the unbalanced potential of said bridgecircuit, indicator means operated by said motor means, and a pair ofcams operated by said motor means, one of said cams varying the forceexerted by said second biasing means upon said member in response to theadjusted position of said motor, and the other of said cams varying theforce exerted by said first biasing means upon said member in responseto the adjusted position of said motor, whereby said indicator means maybe corrected for atmospheric temperature conditions in accordance withthe atmospheric pressure level at which said temperature measurement ismade.

6. A device of the character described, comprising, in combination, amember movable in response to atmospheric pressure, a variablereluctance bridge circuit, a magnetic core mounted on said member andmovable therewith, said bridge circuit including members inductivelyassociated with said core for cooperating therewith to control theelectrical balance of said bridge circuit, a first biasing means actingupon said member, an atmospheric temperature responsive device forvarying the force exerted by said first biasing means in response toatmospheric temperature conditions, a second biasing means acting uponsaid member, motor means controlled by the unbalanced potential of saidbridge circuit, indicator means operated by said motor means, andadjustment means operated by said motor means for varying the forcesexerted by said first and second biasing means upon said member, wherebyan altitude recorded by said indicator means may represent a readingcorrected for atmospheric temperature conditions at a rate determined bythe atmospheric pressure level for which said altitude reading is based.

7. A device of the character-described, comprising, in combination,atmospheric pressure responsive means, a balanced bridge circuit, saidpressure responsive means causing unbalance of the circuit upon movementof said pressure responsive means from a first position to a secondposition, motor means energized by the unbalanced potential of saidbridge circuit, an indicator means driven by said motor means, firstbiasing means adjusted by said motor means while driving said indicatormeans for returning the atmospheric pressure responsive means from saidsecond position to said first position for balancing perature responsivemeans causing unbalance of said circuit upon movement from said firstposition to said second position, and second biasing means adjusted bysaid motor means while driving said indicator means, said second biasingmeans being operatively associated with said temperautre responsivemeans for removing unbalance of said circuit due solely to said movementof said temperature responsive means.

8. A device of the character described, comprising, in combination,atmospheric pressure rebalanced bridge circuit, said means from a firstposition to a second position, motor means energized by the unbalancedpotential of said bridge circuit, an indicator means driven by saidmotor means, first biasing means adjusted by said motor means whiledriving said indicator means for returning the atmospheric pressurresponsive means from said second position to said first position forbalancing said bridge circuit, temperature responsive means movable froma first position to a second position in response to temperature change,connecting means whereby said change in position of said temperatureresponsive means may cause unbalance of said circuit, further meansdriven by saidmotor means while driving said indicator means, saidfurther means including a cam and means operatively associating said camwith said connecting means for removing unbalance of said circuit duesolely to said movement of said temperature responsive means.

9. .A device of the character described, comprising, in combination, avariable reluctance bridge circuit, a pivotally mounted first member, apivotally mounted second member, said second member positioned in spacedrelation to said first member, and means for separately pivotallyadjusting each of said members in relation to the other of said members,said members comprising inductive impedance means included in saidbridge circuit and means reluctively altering the relative impedances ofsaid impedance means, whereby upon variationin the relationship of saidmembers said' bridge circuit may be unbalanced.

10. A device of the character described, comprising, in combination, avariable reluctance bridge circuit, a pivotally mounted first member, asecond member pivotally mounted on said first member, and control meansfor pivotally adjusting each of said members in relation to the other ofsaid members, said members comprising inductive impedance means includedin said bridge circuit and means reluctively altering the relativeimpedances of said impedance means, whereby upon variation in therelationship of said members said bridge circuit may be unbalanced.

11. A device of the character described, comprising, in combination, a,variable reluctance bridge circuit, a pivotally mounted first member. asecond member pivotally mounted on said first member, atmosphericpressure responsive means for pivotally adjusting one of said members inrelation to the other of said members for varyin the impedance of saidbridge circuit, and atmospheric temperature responsive means forpivotally adjusting the other of said members in re-- lation to said onemember, said members comprising inductive impedance means included insaid bridge circuit and means reluctively altering the relativeimpedances of said impedance means, whereby upon variation in therelationship of said members said bridge circuit may be unbalanced.

12. A device of the character described, comprising, in combination, avariable reluctance bridge circuit, a first member, a second memberpositioned in spaced relation to said first mem-- ber, atmosphericpressure responsive means for biasing said first member in such a manneras to adjust the relation of said first member to said second member,and separate atmospheric temperature responsive means for biasing saidsecond member in such a manner as to adjust the relation oi said secondmember to said first member, said members comprising inductive impedancemeans included in said bridge circuit and means reluctively altering therelative im 0! said impedance means, whereby upon variation 7 in therelationship of said members said bridge circuit may be unbalanced. 7

13. In an altimeter the combination comprising a bridge circuit,atmospheric pressure responsive means for causing unbalance of saidbridge circuit, atmospheric temperature responsive means for causingunbalance of said bridge circuit, motor means energized upon theunbalancing of said bridge circuit, first means driven by said motormeans for varying the eiiect of said atmospheric pressure responsivemeans upon said bridge circuit, second means driven by said motor meansfor varying the cited. 0! said atmospheric temperature responsive meansupon said bridge circuit, and altitude indicator means adjusted by saidmotor means, said first and second means being driven by said motormeans so as to cause the rebalancing of said bridge circuit forterminating the operation of said motor means.

14. In an altimeter, the combination comprisins. an atmospheric pressureresponsive means, spring tension means biasing said atmospheric pressureresponsive means in one direction, afirst 'vm s eioree'oisaidspringtension means, a second cam for varying the force of said spring tensionmeans, atmospheric temperature responsive means for adjusting the forceof said spring tension means, and power means for adlusting said firstand second cam means, said power means controlled by said atmosphericpressure responsive means.

'15. In an altimeter, the combination comprising, atmospheric pressureresponsive means, biasing means acting upon said atmospheric pressureresponsive means, variable cam means for adjusting the force exerted bysaid biasing means upon said atmospheric pressure responsive means, andseparate temperature responsive means for adjusting independently ofsaid variable cam means the force exerted by said biasing means uponsaid atmospheric pressure responsive means.

16. In an altimeter, the combination comprising, an atmospheric pressureresponsive member movable from a first to a second position, biasingmeans acting upon said atmospheric pressure responsive member, variablecam means for adjusting the force exerted by said biasing'means uponsaid atmospheric pressure responsive member, separate temperatureresponsive means for independently adjusting the force exerted by saidbiasing means upon said atmosphericp'ressure responsive member, andpower means controlled by said atmospheric pressure responsive memberfor adjusting said variable cam means in such a manner as to cause thereturn of said atmospheric pressure responsive member from said secondto said first position. I

17. In an altimeter, the combination comprising, an atmospheric pressureresponsive member movable from a first to a second position, a leafspring bearing upon said atmospheric pressure responsive member at apoint intermediate the opposite ends thereof, said leaf spring fixedlymounted at one end, a temperature responsive means connected at theotherend of said. leaf spring for adjusting the biasing force exerted therebyupon said atmospheric pressure responsive member, a pair of variablecams, one of said cams bearing upon said leaf spring at a point at oneside of said atmospheric pressure responsive member and the other orsaid cams bearing upon said leaf spring at a point at the other side '0!said atmospheric pressure responsive member, said cams adjusting thebiasing force exerted by said leaf spring, and power means for adjustingsaid cams so as to cause the return of said atmospha-ic pressureresponsive member from said second to said first position, said powermeans being controlled by said atmospheric pressure responsive member.

PAUL F. SHIVERS.

